Signal Routing Problem (Mutiple Audio Interfaces, MacOS)

Here’s what I posted over on the UAD Forum several days ago:

"Cast of Characters:

Mac Studio: M2 Max, Ventura 13.5
UAD Apollo X8p
UAD Apollo X4
UAD-2 Satellite (Octo)
Neve 5057 Summing Mixer
Cubase 13 Pro

The three UAD devices are daisy chained via quality Thunderbolt cables…X8p first, Satellite second, and X4 last.

I have Cubase configured such that all audio channels feed into stems. There are 8 stems…stems 1 - 4 are mono and feed into the X4; stems 5 - 8 are stereo and feed into the X8p. All stems are then supposed to feed into the summing mixer.

My problem is that stems 1 - 4 are not actually feeding into the X4.

I have 2 audio tracks playing keyboard parts, and they are set in Cubase to feed into stem 5. In Cubase’s Studio/Audio Connections/Outputs tab, stem 5 is set to output to A LINE 1 and A LINE 2. (Because I have 2 Apollos, Cubase has named them A (the X8p) and B (the X4).

This works exactly the way it’s supposed to. I can see on the X8p’s front panel meter that this signal is reaching the X8p. From there it hits the summing mixer, as evidenced by the fact that its front panel lights flash.

But I also have an audio track playing a kick drum, and it is set in Cubase to feed into stem 1. In Cubase’s Studio/Audio Connections/Outputs tab, stem 1 is set to output to B LINE 1, in other words the first line input of the X4.

But it doesn’t do this. Looking at the front panel of the X4, I see no movement on the input level meters. However, looking at Console, I see a signal corresponding to the kick drum appearing on the X4’s VIRTUAL 1 channel. So although I’ve set stem 1 to output to the X4’s LINE 1 input, it is in fact somehow making its way to the X4’s VIRTUAL 1 channel in Console. I have to admit that I don’t understand this at all.

I also have a snare drum track feeding into stem 2, with the intention that it will reach the X4’s LINE 2 in, but it instead shows up on the X4’s VIRTUAL 2 channel. Likewise, the bass track I’m sending to stem 3 ends up in the X4’s VIRTUAL 3 channel.

For the mono stems I’m using in this Cubase project (stems 1 -3), I can see signal in the X4’s monitor meters, but NOT in the X4’s Input meters.

What am I missing here? Why for example, when I have a signal set to go to the X4’s LINE 1 input, is it instead showing up in the X4’s VIRTUAL 1 channel?

This is probably something relatively simple, but I can’t figure it out.

Thanks for your assistance."

I’m still trying to figure this out, but I’m stymied as to why a signal is flowing from Cubase into Console. My understanding is that it should be the other way around…Console into Cubase.

And why, when I’ve set stem 1 (for example) to feed into the x4’s LINE 1 input, does it end up in Console’s VIRTUAL 1?

I received the following reply to my initial inquiry:

"Have you referenced the I/O Matrix in Console to see if Core Audio channels are set as expected. You can change the order of Apollo outputs as they corresponds to Core Audio output numbering.”

I replied that I had this set correctly.

After that I decided to focus on Cubase. I chose Studio/Studio Setup, and found that many of the routing assignments were incorrect. Specifically, output port B VIRTUAL 3 was set to show as B LINE 1. I’m a bit challenged when it comes to I/O, but it seemed to me that this could be the problem. IOW, when I thought I was choosing B LINE 1, I was actually choosing B VIRTUAL 1.

So I changed all of the incorrect assignments, but the problem remained. I then exited Cubase and rebooted the computer, but again, the problem remained.

Btw, this used to work on my W11 PC, but I’ve switched over to Mac, and this is my first time trying to use stems on it.

I’m hoping someone can give me a clue as to the cause of this problem.

Screenshots are attached.